IV 



VARIATION 

 BY HUGO DE VRIES, 



Professor of Botany in the University of Amsterdam. 



I. 



Different kinds of variability. 



BEFORE Darwin, little was known concerning the phenomena of 

 variability. The fact, that hardly two leaves on a tree were exactly 

 the same, could not escape observation : small deviations of the same 

 kind were met with everywhere, among individuals as well as among 

 the organs of the same plant. Larger aberrations, spoken of as 

 monstrosities, were for a long time regarded as lying outside the 

 range of ordinary phenomena. A special branch of inquiry, that of 

 Teratology, was devoted to them, but it constituted a science by 

 itself, sometimes connected with morphology, but having scarcely 

 any bearing on the processes of evolution and heredity. 



Darwin was the first to take a broad survey of the whole range 

 of variations in the animal and vegetable kingdoms. His theory of 

 Natural Selection is based on the fact of variability. In order 

 that this foundation should be as strong as possible he collected all 

 the facts, scattered in the literature of his time, and tried to arrange 

 them in a scientific way. He succeeded in showing that variations 

 may be grouped along a line of almost continuous gradations, 

 beginning with simple differences in size and ending with monstro- 

 sities. He was struck by the fact that, as a rule, the smaller the 

 deviations, the more frequently they appear, very abrupt breaks in 

 characters being of rare occurrence. 



Among these numerous degrees of variability Darwin was always 

 on the look out for those which might, with the greatest probability, 

 be considered as affording material for natural selection to act upon 

 in the development of new species. Neither of the extremes complied 

 with his conceptions. He often pointed out, that there are a good 

 many small fluctuations, which in this respect must be absolutely 



